Question

如何设计范围方法让它实际放入row.city？

row.scope do 
  puts city
end

Answer 1

使用instance_eval：

class RowClass
  attr_accessor :city

  def scope(&blk)
    instance_eval(&blk)
  end
end

row = RowClass.new
row.city = "bla"

row.scope do 
  puts city # prints "bla"
end

Answer 2

class Object
  def scope(&block)
    instance_eval(&block)
  end
end

Thing = Struct.new(:city)
row = Thing.new "Bryn Athyn"

row.scope{ puts city }
#=> Bryn Athyn

如果你不想猴子修补对象，你可以选择：

module Scopeable
  def scope(&block)
    instance_eval(&block)
  end
end

Thing = Struct.new(:city)
row = Thing.new "Bryn Athyn"
row.extend(Scopeable)

row.scope{ puts city }
#=> Bryn Athyn

尽管如此，也许最容易的只是：

class Object
  alias_method :scope, :instance_eval
end

或者更容易......只需使用“instance_eval”而不是“scope”：）

调用实例方法而不通过Ruby元编程指定实例？

2 个答案: